Americans who make less money are more likely to suffer from pain than their wealthier counterparts, researchers have found. In a recent study, more than 4,000 people kept a diary of their feelings of pain. Investigators found that those who made less than $30,000 per year reported moderate to severe pain 20 percent of the time, while those who made more than $100,000 per year said they suffered pain less than 8 percent of the time. Researchers say these differences may be because people who make less often have more physically demanding--and pain-inducing--jobs, or they are unable to work enough to have higher incomes.